interoperability meeting s. derriere, strasbourg, 2003 october 16-17 ucd2... when all you have is a...

Interoperability meeting S. Derriere, Strasbourg, 2003 October 16-17

UCD2...When all you have is a hammer...... every problem looks like a nail.

Registry, service description

Problems in the VO:

Resource discovery

Combine heterogeneous data

Answer=UCD ???


● UCD2 are motivated by practical needs.● It is not an attempt to build an absolute abstract vision of astronomy.

UCD should ensure interoperability between VO components:

● Do you have this quantity?● Can I compare this and that?

Standardized description of quantities, between:

● Fuzzyness of natural language● Specificity of data models


Building UCD2

We need something working. Quick.

Conciliate 2 different views:● Bottom-up: describe what exists (VizieR, FITS headers...)● Top-down: global coherence, UCD3 in mind

Concept Property

Class

Instance

Idea of a galaxy Velocity

M31 120 km/s

UCD here


Building UCD2

In UCD2: the primary word describes a property

Major problem: what is a property ? This can depend on the context. This can depend on the use case.phys.velocity

phys.velocity,srcstat.error,phys.velocity,src


Use case

What is the price of a red apple ?

Query expressed in user's terms.

Analyse the query:

●We must find a value for a property: price●We have additional constraints:

●Fruit type must be an apple●Color must be red


Use case

What is the price of a red apple ?

Query expressed in user's terms.

Find resource, and ask query:

SELECT item.price FROM resource WHERE item.fruit.type='apple' AND item.color='red'

UCD Not UCD


Now, what do resources look like ? (resource discovery and querying)

Price Coloritem.price item.color0.19 green0.25 yellow0.39 red

Fruit Price Coloritem.fruit.typeitem.price item.colororange 0.50 orangegrape 0.75 violetapple 0.39 red... ... ...

item.fruit.type='apple'

apples


Description of resource is critical...

●<PARAMETER> in VOTable : addition of a value to a <FIELD> (with associated UCD)● <GROUP>ing of fields, parameters

●No UCD for src.star, or src.galaxy, but src.class exists (concept/instances)●src.class='star' src.class='galaxy'●Need for a normalized vocabulary for objects types (thesaurus more than UCD)

star, late-type stars, early-type starsvariable stars, binary stars...galaxies, AGN, BL Lac, ...


●Need for useable description of parameters in tables.●UCD for instances of photometric bandpasses/filtersThis is not completely satisfying, but we

need it to compensate uncomplete descriptions !

Because we don't have the complete information:●<FIELD>: Column name= Vmag Unit = mag●Related <PARAMETER> :

ID,instr.bandpass= 'V filter'

We use:●Column name= Vmag●Unit = mag●UCD= phot.mag;em.opt.V


UCDFilters, bandpasse

s

UCDObjects types

Data Modelsutype

DALTranslation Layer

VOQL

VOTable

Registry


Complex quantities

Complex = resulting from combination of basic properties. Maths +-/*...

Is it relevant to describe this with words ?

e.g. Color indices: B-V●should we define phot.colorIndex.B-V ? (but what about B-K, J-H, V-I, ...)●or do we allow something like (phot.mag;em.opt.B)-(phot.mag;em.opt.V)

interoperability meeting s. derriere, strasbourg, 2003 october 16-17 ucd2... when all you have is a...

Documents